Compal uses a distinct lettering system: PU for Power ICs, PD for Power Diodes, PR for Power Resistors, and PQ for Power MOSFETs. Standard logic or signal components omit the 'U' or 'R' prefix or use standard variants like U , R , and Q .
The top layer of the LA-C781P schematic acts as the roadmap for the entire motherboard. It highlights how the core chips communicate via various high-speed buses. lac781p schematic top
The voltage passes through two N-channel isolation MOSFETs managed by the charging IC (often a BQ-series chip). If these MOSFETs fail or short to ground, the board will remain completely dead. Always-On Regulators (3V/5V Standby) Compal uses a distinct lettering system: PU for
Board repair history shows that the LA-C781P commonly suffers from specific, reproducible circuit failures: 1. Charging IC Failure ( ACDRV Drop) It highlights how the core chips communicate via
Missing primary systemic voltages or a corrupted firmware payload.
This section is the "heart" of the repair process. It details the generation and flow of all major voltages, starting from the main DC-in (19V) from the adapter to the final low-voltage core rails.
The main 19.5V distribution line that feeds all major step-down Buck switching regulators on the motherboard. Phase 2: Always-On Power Rails (G3 to S5 State)